This project will test whether a standard diagnostic method used in a new clinical setting will locate otherwise elusive, well-differentiated thyroid cancers in 40% or more of affected patients. Twenty patients will be studied; they will: have been previously treated for well- differentiated thyroid cancer, have no residual cancer by conventional tests except that their serum thyroglobulin levels will be elevated. They will be evaluated the residual tumors by scintigraphic imaging one day after injection of the radiopharmaceutical, 111-In-octreotide. When possible, the imaging method will be repeated in the hypothyroid state to see whether this approach provides more sensitivity in finding the cancers. Abnormalities on the images will be confirmed as tumors by ultrasound, CT and/or biopsy/excision. Histologic patterns of previously exicised primary and metastatic tumors will be reviewed to determine if the patterns will predict the scintigraphic results.